Investigations of novel polymorphs of ZnO for optoelectronic applications

Being a promising candidate in next-generation optoelectronic applications, the study of new polymorphs of zinc oxide (ZnO) is receiving the great attention of researchers. In this article, we explore optoelectronic properties of seven polymorphs of ZnO such as wurtzite type, sphalerite type, germanium phosphide (GeP) type, 5-5 type, nickel arsenide (NiAs) type, 5-beryllium oxide (BeO) type and cesium chloride (CsC1) type by using full-potential linearized augmented plane wave plus local orbital (FP-L(APW + /o)) method within Density Functional Theory (DFT). TranBlaha modified Becke-Johnson potential (TB-mBJ) along with Generalized Gradient Approximation (GGA) proposed by Perdew-Burke-Ernzerhof (PBE) as exchange-correlation has been used for the calculations of electronic and optical properties of seven polymorphs of ZnO. Our band structure calculations reveal the considered polymorphs of ZnO as wide bandgap semiconductors. The calculated band gap values of wurtzite type, sphalerite type, GeP type, 5-5 type, NiAs type, BeO type and CsC1 type polymorphs of ZnO are 2.901 eV, 2.679 eV, 2.648 eV, 3.127 eV, 2.986 eV, 3.040 eV and 1.853 eV respectively. The wurtzite type, sphalerite type, 5-5 type, NiAs type, and BeO type polymorphs of ZnO exhibit direct bandgap while GeP type and CsC1 type polymorphs show indirect bandgap. The optical spectra of these polymorphs of ZnO reveal different reflection, plasmon energies, optical absorption, and refractive indices are considerably anisotropic and present different values in the x- and z-direction. The z-component of the reflectivity and absorption spectra was found larger than the x-component in wurtzite type, 55 type and NiAs type polymorphs of ZnO, showing that large reflectivity and optical absorption along z-axis than the x-axis in these polymorphs. This study is believed to provide an interesting guideline for the low-cost and non-toxic new polymorphs of ZnO in cuffing-edge optoelectronic applications.